PWM signals are used in a variety of applications. Some examples of typical applications include controlling motor speed, controlling lighting intensity, and controlling the movement of a gage pointer to name just a few.
Pulse width modulation is the changing of a signal's duty cycle within a fixed period. The resolution of a PWM signal is defined by the number of different duty cycles in the signal and the number of steps at which the signal transitions within a period. For example, a PWM signal having a duty cycle of 50% is on half of the time and off half of the time while a PWM signal having duty cycle of 75% is on three-quarters of the time and off one-quarter of the time. The number of steps at which the signal transitions within a period is its resolution, 2n. A PWM signal having 8-bit resolution can have 256, or 28, different duty cycles, while a 10 bit resolution signal has 1024, or 210, different duty cycle values. High-resolution is typically a resolution greater than 8-bit.
PWM signals are generated using hardware such as a microprocessor integrated peripheral. The peripheral device is limited in the number of PWM signals that it can generate, and is typically limited to four or fewer signals. Hardware is available that can generate more than four signals, but becomes very expensive and therefore, is not always an option for many applications. Many applications for PWM signals require more than four signals, an example being as many as 15 signals that are required for an application such as an automotive instrument cluster. However, a more expensive processor is not necessarily a cost-effective solution for many applications.
There is a need for a simple, inexpensive method of generating high-resolution PWM signals without the need for expensive additional hardware.